The equipment for wells of the aforementioned type generally include a casing bonded to the walls of the well by injecting cement into the annular space. A tubing with a cross section less than a cross section of the casing is taken down into the well as far as the producing zone. It is provided towards the base thereof with one or several packers. The annular space between the tubing and the casing is sealed through the expansion of these sealing parts. The tubing is used for taking the petroleum effluents up to the surface or for various interventions such as, for example, injecting substances into the subsurface formations to stimulate the production.
In a producing well, it is useful to carry out seismic plottings to know the development of the effluent saturation of the oil-bearing strata during the exploitation thereof, and these plottings can be achieved in a particular area of the formation. A method of the VSP (vertical seismic profiling) type may, for example, be implemented, which comprises receiving the waves reflected by the geologic formations or transmitted through them, by several sensors taken down along the well, these waves being transmitted by a seismic generator arranged at the surface or in another well.
It is also sometimes desirable to remove the sensors from a well whose exploitation possibilities prove to be insufficient and to install them in another well. It may be profitable to take advantage of production interruptions which occur on the occasion of maintenance operations, for example, for moving the reception device.
A process and a device for setting up a seismic reception assembly outside, the casing of a well are proposed in U.S. Pat. Nos. 4 775,009 , 4,986,350 and French Application 2,642,849. The process essentially consists in arranging sensors outside the casing, preferably in housings provided to that end,, at the time of the setting up thereof and in surrounding the sensors in the cement that is injected into the annular space between the casing and the walls of the well.
This process has the advantage of facilitating the coupling of the sensors with the formations. On the other hand the irreversible nature of the set up is disadvantageous, the sensors are not recoverable. The permanent immobilization of the sensors is more annoying. It is well-known that, notably with seismic methods of the VSP type, it can be useful to change the position of the assembly of receivers along the well to take into account the modification of the deposit in the course of time, resulting from the production of effluents. Surveying a deposit under production by acoustic waves therefore requires a movable seismic device.
A sonde adapted to be lowered into a well equipped for production and connected to a tubing is is proposed in French Application 2,656,034 and corresponding U.S. Ser. No. 631,253. This sonde comprises an intermediate shoe provided with a central passageway wider than the tubing, arranged between two off centering shoes fixed outside of the tubing. The intermediate shoe comprises a moving device shiftable between a recess position and a position of coupling with the wall of the well under the action of springs, and a housing for sensors and hydraulic triggering means are arranged in the moving device. The device is arranged in such a way that, in the working position, the housing is applied against the wall of the casing and the intermediate shoe is mechanically uncoupled from the tubing.